Fading Immunity to MMR Vaccine May Be Behind the Mumps Epidemic

Hi. My name is Paul Offit. I'm talking to you today from the Vaccine Education Center at the Children's Hospital of Philadelphia.

Last year in the United States, there were 5642 cases of mumps. [Editor's note: These were the case numbers noted at the most recent Advisory Committee on Immunization Practices Working Group meeting on February 22, 2017.] That was the biggest mumps epidemic we've had in a long time, and it included 19 university-based outbreaks. To find out what happened, let's go back to the beginning.

The original mumps vaccine, the so-called Jeryl Lynn strain, was produced by Maurice Hilleman at Merck in 1967. Ten years later, in 1977, it was routinely recommended for all children starting at 12 months of age. Then, because of measles outbreaks that were occurring in the late 1980s and early 1990s, there was a second dose of measles, mumps, rubella (MMR) vaccine recommended in 1989, which gave you then a second chance to get a mumps vaccine.

What we noticed, however, was that 10 years after dose 1, there started to be an increase in the frequency of cases of mumps. Similarly, we're now seeing cases again of mumps 10 years after dose 2—which is to say, in late adolescence and young adulthood. The reason for that could actually be found if you go back and look at those earlier studies. What you find if you do is that the frequency of memory B and T cells for measles and rubella was actually much greater than the frequency of memory B and T cells following mumps vaccination.

That follows what we're seeing now, which is that essentially we eliminated measles from the United States in the year 2000. The reason that we're seeing it come back is that some parents are choosing not to vaccinate their children. And we eliminated rubella from the United States in the year 2005. We've never eliminated mumps.

Some have raised the question of whether this could be due to serology, or that the Jeryl Lynn strain is different enough from the current circulating mumps strains—the so-called G-type strains— that there's been sufficient drift of that strain so that vaccination doesn't protect. But that's not the case. I really think what you're seeing is just fading immunity from what is, frankly, the weaker of the three vaccines.

Now, there is one silver lining in all this. Typically, about 1%-15% of people who have mumps will have aseptic meningitis. Similarly, up to 30% of males will have orchitis. We haven't seen that in the 5600 cases that were reported last year. That's good, because it suggests that at least the mumps vaccine is protecting against the serious sequelae of the disease.

Right now, the Centers for Disease Control and Prevention has created a mumps vaccine working group to investigate whether or not they want to give a third dose of the MMR vaccine at the 11- to 13-year-old platform, along with tetanus/diphtheria/pertussis, meningococcus, and human papillomavirus vaccines. That's in the works, and we'll see what happens over the next year or so.

Thank you for your attention.

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Cite this: Fading Immunity to MMR Vaccine May Be Behind the Mumps Epidemic - Medscape - Mar 17, 2017.